Suspension device of the type mentioned in the introduction are used, as an example, but by no means exclusively, in trucks and similar heavy trucks in order to uncouple the cab from the chassis of the vehicle with respect to vibrations and motions. Since the spring rates of the chassis springs are inevitably high in heavy trucks because of the high vehicle loads, unevennesses of the road surface or even vibrations from axles and the powertrain are still transmitted to the chassis to a considerable extent via the axle spring system.
Cab suspensions in which the cab is supported at the vehicle chassis with the use of a separate suspension system have been developed to minimize the transmission of such shocks and vibrations to the cab and consequently to the driver's workplace in terms of ergonomics and occupational safety for the driver. Due to the fact that the weight of the cab is much lower than the weight of the vehicle, such suspension systems for the cab can be designed with considerably lower spring rates and softer shock absorbers than the axle suspension, and unevennesses and vibrations originating from the powertrain or axles of the vehicle can therefore be isolated or kept away from the driver's workplace considerably better thanks to such cab suspension systems.
However, such suspension device for cabs are of a relatively complicated design, especially if higher requirements are imposed on the absorption of lateral forces or kinematics, for example, the suppression of pitch and roll. Thus, similarly to the case of axle suspensions of motor vehicles, it may often even be necessary to provide additional roll stabilizers, besides the spring and absorber elements proper.
To limit, for example, the undesirable lateral roll of the cab relative to the vehicle chassis, for example, during slant travel or travel in a curve, but, for example, also in case of unevennesses on one side of the road surface, roll stabilizers in the form of torsion bars, by which the shock absorber strokes of the suspension elements of the cab, which elements are the left and right suspension elements relative to the direction of travel, can be coupled with one another to a certain extent, are frequently necessary in suspension device according to the state of the art. However, such torsion bars are, first, highly stressed components, which therefore tend to be expensive.
In order to additionally also prevent or absorb motions or vibrations of the cab in the lateral transverse direction, it is frequently also necessary to provide additional spring/absorber units in the transverse direction of the vehicle, or roller guides for guiding the cab in the vertical direction of motion. Roller guides for limiting the transverse motion are, however, complicated and therefore expensive and, moreover, they have a high maintenance requirement. In addition, such roller guides are often susceptible in terms of fatigue strength and, moreover, they often entail rather substantial noise generation, which in turn has a disadvantageous effect on the ergonomics of the driver's workplace, which should actually be improved.
By contrast, motion absorbers arranged in the transverse direction of the vehicle are inevitably limited to being able to absorb dynamic lateral forces only. By contrast, lateral absorbers are ineffective due to their design in case of quasistatic loads as they develop, for example, during prolonged travel in curves or slant travel.
The devices known from the state of the art for suppressing rolling motions and for absorbing motions of the cab in directions other than in the principal shock direction are therefore of a complicated design, especially because of the high loads acting and, moreover, as was already explained, they have limited suitability.